Induction hardening



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INDUCTION HARDENING Filed Nov. 1'? 1955 4 I 4 Sheets-Sheet 1 F/G./ Z5

- INVENTOR smqu l. J1 LORI/VG ATTORNEY March 4, 1958 Filed Nov. 17, 1955 S. J. LORlNG INDUCTION HARDENING 4 Sheets-Sheet 2 jiw% INVENTOR SAMUEL J. LOR/NG ATTORNEY March 4, 1958 5. J. LORING 2,825,788

- INDUCTION HARDENING Filed Nov. 17, 1955 4 Sheets-Sheet 3 ma I INVENTOR SAMUEL J. LOR/NG ATTORNEY March 4, 1958 5. J. LORING 2,825,788

INDUCTION HARDENING Filed Nov. 1'7, 1955 4 Sheets-Sheet 4 INVENTOI? SAMUEL .1 LORING BY m *2 M ATTORNEY barrel.

United States Patent INDUCTION HARDENING Samuel J. .Loring, West Hartford, Conn, assignor to United Aircraft Corporation, 'East Hartford, Conn., a

corporation of Delaware .Application November'17, 1955, Serial No.-547:,496

'3 Claims. '(Cl. 219-10.41)

invention relates to induction heating and particu- ..larly to aheating head for an induction .hardeningqmachine.

:An object of this invention is an improved heating rhead producing a uniform heating pattern witha smaller amount of energy.

A .further object is a heating head having movable conductor means which may be placed close to the work :piece'to behardened.

A still further object is a heating head inductively transferring current from a'fixed conductor to amovable conductor adjacent the work piece.

Anotherobject is a heating head inductively transferiring current from a .fixed conductor to a plurality of imovable conductors which may be moved into grooves Lina work piece to be hardened and having means .for

cooling the conductors and cooling the work pieceafter :heating.

Other objects and advantages will be apparent from :the following specification and the accompanying drawings in which:

Fig. 1 is a rear elevation of a hardening machineshowing the heating head in position for heating'the inboard race of an-aircraft propeller hub.

Fig. 2 is a side elevation partly in section of aportion of the machine showing further details of the heating head.

Fig. 3 is a sectional view of the heat head taken on twoplanes at 90 to each other and intersecting-at the longitudinal center line and showing the secondary conductors in their retracted position.

Fig. 4 is a sectional view similar to Fig. 3 showing the secondary conductors in an extended position.

Fig. 5 is a schematic view to illustrate the theory of :operation of the heat head.

Fig. 6 isa top view of the segments.

In the heating of ball bearing races in propeller hub blade sockets for the purpose of hardening the races where-the hardening is done after the races have been "formed in the barrel, it becomes necessary to heat the bottom of the ball race groove. One way in which this may be done if sufficient power is available is by inducing current along a meridian of the surface by means of conductors arranged in the meridian plane and rotated about thecenter line of the hub barrel socket was to eventually heat the entire inner surface of the socket. This, however, requires a machine having sufficient power to heat all the races'at once by inducing currents longitudinally of the blade socket, and does not give 'accurate controlof the heat pattern.

This present invention relates to aheating head by "means of which a single race can be heated throughout its periphery and the desired heat patern imparted to the In order to heat the bottom of the race and not burn the lands between the races, it is necessary to place a conductor close to the bottom of the race and this will requiresome sort of expansible conductor. Applicant has found that by using a 'secondary conductor .made up 2,825,788 Patented Mar. 4, 1958 or segmentswhichtogether make a complete but interments and from the secondary conductorsegments to the barrel races and provide a nicely controlled, uniform pattern of heating and hardening.

In the drawings the heat head,-which'is shown generally at 10,-is secured ton-pedestal '12 of arnachine comprising 'a base 14 and'rods 16 extending upwardlyfrom the base. A cross arm 18 is mounted'to slide vertically on the rods 16 and "carries-a sleeve20 mounted in ball bearings for rotationinthe arm 18. -A -bolt 22 extending through sleeve 20 has 'anut 24 on-the lower end thereof by means of Whichanairplane propeller hub 26 may be secured 'to the sleeve 20 for rotation therewith. The

arm 18 with-the barrel secured thereto may be raised by means of the ring 28-and lowered'by-gravity. When the hub is lowered, the lower hub arm rests on a sleeve 30 mounted on roller bearings 32 and 34 which support the barrel for rotation about the'longitudinal axis of the barrel arm and also serve to center the barrel with respect tothe heat head. Wedges 36 may be used to center the barrel with-respect to the-sleeve 30. The barrel may be raised by means'of'the-ring 2810 a position abovethe heat head 10, and sleeve '30 may be'replaced with a sleeve having a larger longitudinal dimension so that when the barrelis again'lower'ed-over the heat head to "rest on the sleeve -30, the'heathead conductors will be positioned against "a different bearing race so that the bearings may beheate'd-and hardened'consecutively one at a time.

The heat'head 10 comprises a metal sleeve 38 which is mounted on the pedestal '12, and-secured thereto by cap screws, not shown. A'metalsleeve '40 having a threaded portion 42 at the upper end thereof, threads into a head block of insulatingmaterial 44 having guides 43, 45 for the supports for the secondary conductors 46 and '48. The primary conductor 50 seats in a recess 52 in the block 44'and rests on an insulating ring 54 which in turn --rests on another insulating ring 56. Ring 56 rests on a flange 58 of a shorting ring-60 which in turn rests on an insulating ring 62 which rests on an insulating sleeve Metal sleeve 40 rests on, and is secured by, cap screws to shelf 66 extending inwardly from sleeve 38. Sleeve '40 thus acts to secure head block 44 to sleeve 38 and clamp conductor 50, insulating rings 54 and 56, conductor 60, and insulating rings 62 and 64 between the head block and the shelf 66, and thus secure the series of elements in assembled relation to 'the sleeve 38.

In order to assist in making the assembly secure, sleeve 64 is cemented to sleeve 38 and sleeve 49 is cemented to head block 44.

Primary conductor 50 is shaped'into'circular form. A

insulated from each other and connected to separate bus bars 68 and 70, which in turn are connected to a source of alternating current. The bus bars 68 and 70 are separated by insulating material and are made hollowgso as to conduct a cooling medium, such as water, to the primary conductor 50 for circulation therethrough. Pipes 72 and 74 serve as a means for introducing and withdrawing a coolant to andfrom the bus bars.

The secondary conductor comprises a series ,ofsegments of any desired number, four being utilized in the embodiment selected to illustrate this invention.

Segments 46 are supported on slides or extensions 76 fitting into slots 45 in the insulating head block 44 and segments 48'are supported on slides orextensions 78 fitted into slots 43 in the head block 44. The slots 45 forseg- -ments '46 are arranged at-about a 30 angle, andthe-slots 43 for slides '78 are-arran'ged at about 'a '45 angleso'that surface of the ball bearing groove.

segments 46 may be slid downward and outward into position and then segments 48 may be slid downward and outward into position between the segments 46 and closely adjacent thereto although still insulated from, and spaced from, segments 46. A knurled nut 80 carries a pivot 82. A link 84 of insulating material connects pivot 82 with a pivot 86 carried by the extension of conductor 46. Nut 80 is threaded onto a stem 88 so that rotation of the nut will cause it to travel up or down the stem and thus retract or extend conductors 46.

Conductors 48 may be similarly actuated by a knurled nut 90 connected by means of an insulating link 92 with the conductor 48.

Segments 46 and 48 are made hollow with several cooling water passages therein. Cooling water is led to and from segments 46 by pipes 94 and to and from segment 48 by pipes $5. Each of the segments 46 and 48 have an undersurface which mates with the upper surface of primary conductor 50. In their extended positions the segments 46 and 48 are spaced from primary conductor 50 by insulating surfaces 96 and 98 so as to accurately maintain the lower surface of the segments mating with, close to, but spaced from, the upper surface of the primary conductor.

As shown in Fig. 2, the outer ends of the segments 46 and 43 are shaped to conform to the shape of the bottom of the ball race grooves and when extended are positioned adjacent to but spaced from the bottom of the grooves of the ball bearing races.

A shorting ring 60, which may be supplied with a cooling fluid in any desired manner, not shown, is located adjacent the land between two adjacent ball races to prevent overheating of the land. This comprises a closed ring of conducting material such as copper.

As shown in Fig. 5, the primary conductor 50 is supplied with alternating current of a frequency which will give the desired penetration and hence, the desired depth of heating. In one particular embodiment, we have found that a frequency of approximately ten thousand cycles per second has given a desired penetration of about 3 of an inch. The segment, which may be any one of the four segments which have been indicated as 46, 48 arranged adjacent to primary conductor 50, has a current induced therein. As the segment is completely insulated from both the primary conductor 50 and the work piece but is adjacent to both of them, there will be induced in the segment a current circuit which runs near the surface of the segment adjacent to primary conductor on one side and adjacent to the ball race on the other. Current flow in the portion of this circuit adjacent to the primary conductor is induced by the primary current and the induced current in the return portion of the circuit adjacent to the ball race in turn induces current in the latter. In other words, a sort of eddy current is set up in the segment. This occurs in a similar manner in each of the segments, which, being adjacent the bottom of the groove of the ball races will set up in the hub socket and, particularly in the ball bearing race, a current in a circumferential path around the hub socket with the current concentrated adjacent the This induced current in the hub socket will heat the groove and it has been found that it will heat the groove quite uniformly and to the desired depth and in the desired pattern.

In practice, the barrel is rotated slightly during the time, in one embodiment about 12 seconds, that the socket is being heated, so as to insure an even heating and avoid any possibility of variations in the heat due either to manufacturing tolerances or the slight gaps between the segments.

The shorting ring 66 arranged near the land between two adjacent ball races is designed to draw the field away from the corner of the land to prevent overheating of the land and prevent heating of the adjacent race.

A cap of insulating material comprising the two mating elements 100 and 102 is secured to the head block 44.

The two parts 100 and 102 of the cap, when assembled, form a channel 104 having a plurality of outlets 106 and inlets 108. An insulating block 110 is secured to sleeve 38 and carries a channel 112, which will conduct cooling air from the inlet pipe 114 to the inlets 108 and the channel 104 from which the cooling air is discharged from outlets 106 onto the heated ball races to cool and harden them. Cap element 100 is provided with a metal protecting cover 116. v

In operation of the mechanism, the proper sleeve 30 is positioned on the sleeve 38 and the hub barrel 26 is lowered over the heat head 10 with the secondary conductor segments 46 and 48 retracted. With the barrel in po sition, knurled nut is turned down to extend diametrically opposite segments 46. After the segment 46 has been positioned, either by observation or by manual stop or stops not shown, nut 99 is turned down to extend the diametrically opposed segments 48 and position them between the segments 46 and 48. The segments 46 and 48 are then spaced a short distance, say of an inch from the bottom of the ball races and adjacent to but spaced from and mating with the primary conductor 50, being spaced as close as practical, say about from the primary conductor. The switch is then closed, introducing the high frequency alternating current to the bus bars 68 and 7t and cooling liquid is simultaneously circulated through the several conductors 46, 48, 50, and 60. In one embodiment, currents in the neighborhood of 2000 amperes are passed through the primary circuit for a period of about 12 seconds to heat the barrel races. The amount of current would vary with the size of the article to be treated, and the frequency of the current would vary with the desired depth of heating. the heating period, the electricity is disconnected, and the cooling air is turned on to discharge from the orifices onto the heated race to cool and harden the same. After the race is cooled, nut is backed off to withdraw segment 48 into the elevated position shown in Fig. 3 from the extended position shown in Fig. 4, and then nut 80 is backed off to withdraw segment 46 to the retracted position shown in Fig. 3 from the extended position shown in Fig. 4. The barrel is then lifted olf from the heat head and a different size of spacer ring 30 is installed. The process is then repeated for the next adjacent race. This process is continued until all the races have been hardened.

By thus inducing a circumferential current in the blading socket, it has been found possible to produce a very uniform heat pattern and a very uniform hardened area for the ball races with a minimum of power and equipment.

It is to be understood that the invention is not limited to the specific embodiment herein illustrated and described, but may be used in other ways without departure from its spirit as defined by the following claims.

I claim:

1. In a device for inductively heating at least one of a series of circumferential internal grooves in a tubular work piece, a full turn conductor adapted to be connected across a source of alternating current, a second conductor adjacent said full turn conductor and comprising more than two segments electrically insulated from each other and from said full turn conductor and inductively connected with said full turn conductor so as to induce currents in said individual segments, means for withdrawing said segments radially inward to provide a smaller overall diameter for the combined full turn and segmental conductors to permit insertion of said full turn and said second conductors into the interior of said tubular work piece, means for extending said segments radially outward into one of said internal grooves after insertion into said tubular work piece to form a substantially continuous ring of segments and inductively connect said segments with the periphery of said one groove and induce current in the periphery of said groove from the currents in the individual segments, said seg- At the expiration o f ments having a contour mating with the contour of the portion of the groove to be heated and when extended extending around the entire groove periphery.

2. In a device for inductively heating at least one of,

a series of circumferential internal grooves in a tubular work piece, a full turn conductor adapted to be connected across a source of alternating current, a second conductor adjacent said full turn conductor and comprising a plurality of segments electrically insulated from each other and from said full turn conductor, and inductively connected with said full turn conductor so as to induce currents in said individual segments, means for withdrawing said segments radially inward to provide a smaller overall diameter to permit insertion of said full turn and said second conductors into the interior of said tubular work piece, means for extending said segments radially outward into one of said internal grooves after insertion into said work piece to form a substantially continuous ring of segments and inductively connect said segments with the periphery of said one groove and induce current in the periphery of said groove from the currents in the individual segments, said segments having a contour mating with the contour of the portion of the groove to be heated and when extended extending around the entire groove periphery and means to prevent overheating the land adjacent said grooves comprising a third conductor shorted on itself and located opposite the land adjacent the transverse portion of the groove being heated for reducing the magnetic field effective on said land and reducing the current in said land.

3. The method of inductively heating the perimeter of a groove in the inside surface of a sleeve without unduly heating the land adjacent said groove comprising directing an alternating current in a substantially closed loop, inducing a plurality of adjacent eddy currents from the current in said loop, said eddy currents having one per tion of their paths adjacent and substantially parallel to the current in said loop and another portion adjacent the surface of said groove, arranging said eddy currents adjacent said groove perimeter so that the portion of said eddy currents adjacent said perimeter all run in the same direction around said perimeter, inducing a current in said sleeve around the perimeter of said groove from said eddy currents, drawing off from said land a portion of the current inducing field created by said eddy currents to reduce the heating effect in said land.

References Cited in the file of this patent UNITED STATES PATENTS 2,223,902 Somes Dec. 3, 1940 2,399,897 Somes May 7, 1946 2,643,325 Body et a1 June 23, 1953 FOREIGN PATENTS 650,184 Great Britain Feb. 14, 1951 

